GT40 / GT40P

Got them on mine John,HM exhausts fit fine.

Not impossible, just $$.

P heads have been discussed ad nauseum here... Expect 40hp or so on a 351w. Add another 30-40 with the proper intake and cam to match. 302 numbers won't be quite as high... But a properly built p-headed 302 (cam and intake, 9.5-10cr) and you can approach 290hp or so. This is with the available RH flat tappets. Peak power usually ends up in the 5000-5200 range with a decent cam. Power is added everywhere, from holeshot on up.

Gt40's are more highly regarded in automotive circles as they don't require special headers. Plug angle of the p's are an advantage on our upswept marine manifolds. In addition to slightly better flow, p's also have smaller chambers so they give you about a point of CR over the regular gt40's. Google "ford head flow chart" and you'll see flow numbers of stock e7's, gt40's, p's and many aftermarket heads. That's a better apples to apples comparison than dyno results since so many other aspects of a build can affect hp. Remember that you're limited to .490 lift with flat tappet RH stuff (and that's with 1.7's) so decent flow at lower lift is key. Don't be fooled by big flow numbers in the .500-.700 range as you'll never utilize it.

Thank you Tim. I googled correct craft fans Gt40>40P and read everything that came up. I may be willing to give up the stock manifold on the "spare" but I believe I am am staying with the original flat tappet cam. It concerns me that it raises the CR 1 point since it is 10.5:1 right now. I want to be able to use the 91 marine gas available on my chain. I saw that there is a source out there that some recommended. I would have to rebuild the stock heads anyway so it seems like it would be pretty economical. Do you have any more suggestions. I know some purists may not like it but I can set aside the old heads from this one and store the original engine.

I believe my shop guy said it has teeny chambers. Are you familiar with these?AFR 165cc non smog

Gary, did the heads of the ARP bolts hit the manifolds? How much relief was required to make them fit?

TRBenj wrote: Joe, did you work through Jay Allen with your Trick Flows?

total engine airflow

Did the original bowl work and assembly. They also welded them up after the digested a piece of.the number on piston. Quality and timely work.

John clearance issues were minor,depending on how the nut was clocked after it was torqued determined if clearancing was needed.

john b wrote: Thank you Tim, Gary, Pete and all who helped. I was losing my way a bit and you put me back on track. I talked to Tri State. $598.00. and they install the larger valves. I just need to determine my current chamber size now so I don't exceed what I view as the limit of 10.5:1 that it is now.

Be careful on the spring selection through- ask them if they are ok to use with a flat tappet cam and if there is anything special you should do during cam break in. You can always lower compression with your head gasket selection, although it can get more expensive to specify a fancy cometic gasket with a custom size. You may need to figure out which pistons you have and do the math rather than try and go backwards from what you think the last setup was rated at.

The current crop of available RH blanks are limited to .460 lift at the valve (with stock 1.6 rockers). This cam is about the only flat tappet RH I would consider changing to. Reid is probably the only person who might be able to tell you how that 2v HM cam spec'd out. I would guess it's kinda small, being for a 210hp 2bbl, but that's just a guess. 1.7 rockers might be a consideration instead if a cam swap is deemed unnecessary.

I would call tristate back and see what they say about the sprigs. Iirc, they are on the aggressive side ("up to .550 lift") and you will want to reiterate that you have a flat tappet- and are considering a new flat tappet so break in may be a concern. Wiped lobes are the worst!

Sealed Power still sells the Marine grind cam for the 302, gives a lot of low end torque but has good idle quality. I put one in a friends 68 (4 wheel) Mustang with an automatic trans and tall gears and it ran really well all the way to 5,300 RPM or so. He is very happy with that selection. It is a copy of the grind Pleasure craft used for the 302. I believe they have it RH and LH rotation. I am sure you can get more cam but you may need a custom grind. Reverse rotation limits what is available.

Hi Bri892001. 2V and 4V refer to the carburetor venturis, commonly called "barrels". The 210hp H/M engine, iirc is a 450 cfm 2V, and the 235hp H/M used an Autolite 600cfm 4V. Just a wild guess but I think the 210 probably had more low end torque than the 235 4V, especially since the Autolite was mechanical and not a progressive linkage. It could dump all the vacuum at the flick of a wrist. I'm not an expert but the original 4V doesn't seem well suited to a ski boat to me.

john b wrote: Just a wild guess but I think the 210 probably had more low end torque than the 235 4V, especially since the Autolite was mechanical and not a progressive linkage. It could dump all the vacuum at the flick of a wrist. I'm not an expert but the original 4V doesn't seem well suited to a ski boat to me.

John, I'm not at all familiar with the autolite carbs... But maybe you could explain why you think the 4v might have been a poor performer (at least out of the hole)?

The only boat I've ever seen where you need to be judicious about applying too much throttle out of the hole was Reid's warmed up Royal Flush... In 2bbl form.

That's the first time I've heard of a carb that opens all 4 barrels together. I wonder what the thought process was behind it? Maybe avoid the possible hesitation of secondary's that kick in later?

Dave, my guess is it may be because the cars the C8AE-AF Autolite was installed on were generally either not sold to the general public ( Police Interceptor ) or they were not built by Ford (Shelby GT500 and Holman Moody 428) and little thought was given to anything but driving with the loud pedal down. At high rpm power settings I believe this configuration would offer better throttle response and it would be more linear. I'm a hack skier and all I like is a hard smooth pull out of the hole, not instant response at 3000rpm. Is there any use for that in a ski boat? I don't know, I'm just an over the hill hack skier. In the interest of safety I'm not going to use the Autolite, it's not a marine carb. I have a marine Holley 600 that's going on there.

If anyone is interested I saw a listing for GT40 heads used on Craigs List Sacramento. $200. for the set. Probably need a valve job after purchase but a good find for someone.